The Conservative claim that 4 million people are liable to inheritance tax at a threshold of £325,000, assumes none of them have access to a solicitor. Here's why:
Terry and June, who have two children called Jack and Jill, own a house worth £500,000. If they do nothing, then when Terry dies, June will own the house on her own. No inheritance tax will be due at that stage, but when June dies, Jack and Jill have to pay inheritance tax on the full amount.
However, if Terry and June go to a solicitor, she can do something called "splitting the tenancy", which enables Terry and June to each leave their half of the house to their children. So, after Terry's death, June owns half the house, while Jack and Jill each inherit a quarter of the house from Terry. No inheritance tax is payable because Terry's share of the house, valued at £250,000, is below the inheritance tax threshold. When June dies, her half of the house is also left to Jack and Jill, but since it is also worth £250,000, it is still below the inheritance tax threshold.
So the Tory claim should be amended to 4 million people are liable to inheritance tax, but only if they don't trust their spouse, or their children, or have a phobia about lawyers.